ABSTRACT
Chemically vapor-deposited (CVD) polycrystalline diamond films are being considered for use as protective films on high-wear surfaces. One of the critical issues in this regard is the adhesion between the diamond film and the underlying substrate material. An understanding of the diamond film-substrate bond strength and how it can be improved is therefore of considerable importance. Very few studies dealing with the measurement of adhesion between CVD diamond films and substrate materials have been published and all of them are very recent. Adhesion measurements of diamond films are complicated by the very properties of diamond films that are desirable-high hardness, well-defined grain structure, and resistance to mechanical damage. Several research groups have presented quantitative data on adhesion based on the cutting life of diamond-coated tool inserts [1-3], the wear of diamond film surfaces as measured by the pin-on-disk method [4], and the resistance of films to erosion by impact with sand particles [5]. Other groups have used more direct methods for
the quantitative determination of diamond film-substrate pair adhesion, such as scratch testing [6], tensile pull testing [7, 8], and indentation testing [9-11]. Since the adhesion measured by the above-mentioned tests is dependent on a wide variety of variables, the measured value is called the practical adhesion [12]. It is not a fundamental quantity, but it can be useful for comparison purposes. Although considerable progress has been made, systematic studies dealing with the quantitative measurement of the adhesion of diamond films to various substrate materials and correlations with deposition variables have yet to be reported. Such studies are extremely important in arriving at some general guidelines for synthesizing diamond films which exhibit optimum adhesion to the substrate. In this paper, we present adhesion data obtained by tensile pull testing for CVD diamond films on tungsten. The diamond films were prepared by a hot filament-assisted process for a range of critical deposition parameters. The objective of the study was to determine how the adhesion of diamond films on tungsten varied with the processing parameters, with the ultimate goal of establishing the optimum set of conditions for growing diamond films on tungsten with good adhesion.
